knjiga solarna energija dobra

792 PHOTOVOLTAIC SYSTEMS
operate completely autonomously, the supply reliability is decisive, whereas this issue
is of secondary importance for a household supply in which a back-up generator is
included anyway.
The operation behaviour of the photovoltaic system is characterised and evaluated
with the help of a suitable computation procedure. It is particularly important to know
the system’s operation behaviour with regard to the supply reliability and the effective
use of the photovoltaically generated electricity.
The optimal tilt angle for the solar generator depends on the specific conditions
under which the system is operated. A clear distinction must be made between gridconnected
and stand-alone systems. Grid-connected systems are generally optimised to
achieve the maximum possible annual yield. As all of the energy output from the solar
generator is used either by direct consumption or by being fed into the public electricity
grid, the system yield has the same dependence on the orientation and tilt angle as the
solar radiation incident on the solar generator (Figure 17.35).
The optimum tilt angle of about 30 ◦ is smaller than the average solar zenith (equal
to 90 ◦ latitude), as the major share of the solar radiation is incident during the warmer
six months for the Central European climate.
C
FhG-ISE
90
60 65 60
80
70
70
65
60
50
80
95
75
Tilt angle
40
30
90
100
85
20
10
0
−80 −60 −40 −20 0 20 40 60 80
East
Orientation
West
Figure 17.35 Dependence of the annually used solar energy from a grid-connected system dependent
on the orientation and tilt angle (percentage values relative to the maximum used solar energy;
orientation 0 = south, for the northern hemisphere)